The light yield is critical for the TAO GdLS, since we anticipate an energy resolution as high as possible to study the fine structure in the reactor antineutrino spectrum. To predict the light yield of LS with different PPO and bis-MSB concentrations, Geant4 [1]} simulations are done with a simplified detector geometry and a newly-developed optical model [2]}. The optical model takes into account the light emission and absorption processes by PPO and bis-MSB, and is tuned with the measurements in a Daya Bay detector with 12 different configurations on the PPO and bis-MSB concentrations. The predicted light yield curves are shown in Fig. REF . Even assuming the largest possible solubility of 1.2 g/L PPO and 0.5 mg/L bis-MSB in LAB at -50\(^{\circ }\) C, the relative light yield, shown as the red star in the plot, is only 82% of the maximum, that with 4 g/L PPO and 4 mg/L bis-MSB.
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